JPH0225718B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temper bead welding method that reduces the hardness of the welded part to 260H _V or less when welding steel materials with a carbon equivalent of 0.45% or less.

In recent years, large offshore structures such as oil drilling structures used in contaminated sea areas are often required to have welded parts with a hardness of 260H _V or less to prevent stress corrosion cracking.

In general, when welding this type of structure, the welded part is often hardened due to the type of steel (especially carbon equivalent) and welding method (especially welding position), and reducing the hardness is an essential requirement. .

Conventionally, heat treatment such as tempering after welding has been used as a means to reduce hardness, but this requires a great deal of time and effort and is not practical for large structures such as those mentioned above. Further, although it is possible to soften the welding heat input by increasing the welding heat input, an excessive increase in the welding heat input is not preferable from the viewpoint of ensuring low-temperature toughness.

This invention was made to solve the above-mentioned problems in the prior art, and the beads at both toes of the final finishing layer of the welded part are 0.5KJ/m・m~
Welding is performed with a heat input of 3KJ/m・m, and for the part where the heat affected zone is hardened, the next overlapping bead and the final bead are shifted from the previous bead by 1 to 5m・m to 3KJ/m・m. The feature is that the hardened portion of the bead is softened by welding in layers with a heat input of 5 KJ/m·m.

To explain the reason for limiting the numerical values in this invention, the bead heat input at both toes of the final finishing layer is
The range of 0.7KJ/m・m to 3KJ/m・m is as follows.
This is because if it is less than 0.7 KJ/m・m, the welding current must be low and the welding speed must be high, making it impossible to form a bead.
If it exceeds m, the bead itself at both toes will become large, and if the next bead and final bead are welded overlappingly on the bead, the weld overlap will shift by more than 5m・m, so the effect of tempering will not occur. It is. Next, the heat input of the next overlapping bead and final bead on the beads of both toes was limited to 3 to 6 KJ/m・m.If the heat input is less than 3KJ/m・m, This is because tempering cannot be performed and if the temperature exceeds 6 KJ/m・m, the low-temperature toughness of the weld will deteriorate.

Figures 1 to 4 show the results of experiments in which beads were stacked and welded on a flat plate with various heat inputs and bead shifts l, and the hardness was measured.

In Figure 1A, bead 1 corresponding to the toe is shown.
0.5KJ/m・m, 3KJ/m・m for next layer bead 2
, and bead 1 and bead 2 are 8
The welded joint surface when welded with a distance of m·m is shown, and the hardness results in this case are shown in Figure 1B.
As is clear from Figure 1 (b), it exhibits high hardness with H _V of 250 or more. Also, in Figure 2 A, bead 1
0.5KJ/m・m (● mark) and 3.0KJ/m・m
(○ mark) indicates the case where bead 2 is welded at 3KJ/m・m with a distance of 5m・m, but in this case,
As shown in Figure 2B, both beads have a hardness of 260H _V or less. Furthermore, in Figure 3 A, bead 1 is 3.0KJ/m・m, bead 2 is 3.0KJ/m・m・
m (○ mark), and 4.0KJ/m・m (● mark),
The case where welding was performed with a distance of 10 m/m is shown, and in this case, the hardness shows a high result as shown in Figure 3 (b).

Furthermore, as shown in Figure 4 A, bead 1 is 1.3KJ/m・
m, bead 2 1.3KJ/m・m (△ mark), 3.0KJ/
m・m (○ mark), 4.0KJ/m・m (● mark), when welded with a distance of 5m・m. In this case, as shown in Figure 4B, bead 2 is 1.3KJ/
In the case of m・m, the tempering effect is not sufficient due to insufficient heat input, resulting in high hardness, but bead 2 is 3.0KJ/m・
m, 4.0KJ/m・m shows a hardness of 260H _V or less.

The sample materials used in the above experiments all had a thickness of 45 mm.
m・m, 50kg high-strength steel with a carbon equivalent of 0.40% or less, the Bitkers load is 10Kg, and the hardness measurement depth is 1m・m below the surface of the base material.
Incidentally, the horizontal axis of the diagrams in FIGS. 1 to 4 represents the preheating temperature. Conventionally, high-strength steel is preheated prior to welding to prevent defects, but as shown in the figures above, it is clear that in the present invention, welds of 260 H _V or less can be formed even in areas without preheating.

From the above, if the welding heat input is out of the above range, the hardness cannot be lowered to 260H _V or less, and the distance between the toe bead (bead 1) and the next layer bead (bead 2) is 1 It is clear that if the hardness exceeds 5 m/m, the hardness cannot be lowered to 260H _V or less.

FIG. 5 shows an example in which the present invention is applied to an actual welded joint. In the final finishing layer, the toe bead 1 is first placed with a heat input of 3.0 KJ/m·m. Next, add the next layer beads 2 to the toe beads 1 to 1 to 5.
Lay it on the bead 1 with a heat input of 3.0KJ/m・m within the range of 3.0KJ/m・m, then place the other toe bead 1′ with a heat input of 3.0KJ/m・m, and then the final bead. The distance between 2' and the bead 1' is 1 to 5 m.
The heat input was kept within the range of 3.0 KJ/m・m, and it was overlapped on bead 1'. Welding was performed on surfaces A and B under the above conditions.

Figure 6 A shows the hardness measurement positions of the joint welded under the above conditions, and Figure 6 B shows the hardness values. The left side of the figure is the base metal side, and the right side is the weld bead side. Each figure shows the bond part as the center. All values are below 260H _V ,
In particular, we were able to satisfy the hardness in the vicinity of the heat-affected zone of the base metal in the weld surface layer, which is a problem. In addition, the sample material has a plate thickness of 45
m・m, 50 kg high tensile strength steel with carbon equivalent of 0.43%.

According to the present invention, the hardness of the welded portion can be lowered simply by stacking weld beads with a predetermined heat input, so that useful effects such as welding of large structures can be extremely easily achieved.

[Brief explanation of drawings]

Figure 1 A, B to Figure 4 A, B are diagrams showing the cross-sectional view and hardness distribution of the welded part when the bead overlapping distance and heat input conditions are changed. FIG. 6A is a cross-sectional view of a welded part showing an example, and FIG. 6B is a diagram showing the hardness measurement position, and FIG. 6B is a diagram showing the relationship between the distance from the bond part and the hardness. In the drawings, 1, 1', 2, 2'... beads.

Claims (1)

[Claims] 1. In the final finishing layer of the welded joint, weld the beads at both toes with a heat input of 0.7 KJ/m-m to 3 KJ/m-m, and then weld the beads of the next layer and the final bead at a distance of 1-5 m from the said bead.・3KJ/at a point shifted by m
A temper bead welding method characterized by welding in layers with a heat input of m・m to 6KJ/m・m.